1. Field of the Invention
The present general inventive concept relates to an inkjet printhead, and more particularly, to a thermal inkjet printhead in which residual heat generated from a heater is effectively dispersed, thereby enhancing an ink ejecting ability of the thermal inkjet printhead.
2. Description of the Related Art
Generally, an inkjet printhead ejects ink droplets on desired positions of a recording paper in order to print predetermined color images. Inkjet printers are classified into shuttle type inkjet printers having printheads that are shuttled in a direction perpendicular to a transporting direction of a print medium, and line printing type inkjet printers having a page-width array printhead corresponding to a width of a print medium. The line printing type inkjet printer has been developed for high-speed printing. The array printhead has a plurality of inkjet printheads arranged in a predetermined configuration. In the line printing type inkjet printer, during printing, the array printhead is fixed and a print medium is transported, thereby allowing high-speed printing.
Inkjet printheads are categorized into two types according to an ink droplet ejection mechanism thereof: a thermal inkjet printhead and a piezoelectric printhead. The thermal inkjet printhead ejects ink droplets due to an expansion force of ink bubbles generated by thermal energy. The piezoelectric inkjet printhead ejects ink droplets by pressure applied to ink due to a deformation of a piezoelectric body.
The ink droplet ejection mechanism of the thermal inkjet printhead is as follows. When current flows through a heater made of a heating resistor, the heater is heated and ink near the heater in an ink chamber is instantaneously heated up to about 300° C. Accordingly, ink bubbles are generated by ink evaporation, and the generated bubbles are expanded to exert a pressure on the ink filled in the ink chamber. Thereafter, ink droplets are ejected through a nozzle out of the ink chamber.
FIG. 1 is a schematic cross-sectional view illustrating a conventional thermal inkjet printhead. Referring to FIG. 1, the conventional inkjet printhead includes a substrate 10 on which a plurality of material layers are stacked, a chamber layer 20 that is stacked on the substrate 10 and defines an ink chamber 22, and a nozzle layer 30 stacked on the chamber layer 20. Ink is filled in the ink chamber 22 and a heater 14 to heat the ink to generate bubbles therein is installed under the ink chamber 22. In addition, the nozzle layer 30 has a nozzle 32 through which ink is ejected.
An insulation layer 12 for heat and electric insulation between the heater 14 and the substrate 10 is formed on the substrate 10. The heater 14 to heat the ink in the ink chamber 22 to generate bubbles therein is disposed on the insulation layer 12. Conductors 16 for supplying an electric current to the heater 14 are disposed on the heater 14. A passivation layer 18 is formed on the heater 14 and the conductors 16 to protect the heater 14 and the conductors 16.
However, in the above conventional structure, some of the heat generated from the heater 14 is used for ink ejection and the rest of the heat is dissipated to outside of the printhead mainly through ink, and thus an ink dissipation effect is degraded. When the heat generated from the heater 14 is accumulated around the ink chamber 22, a temperature of the ink filled in the ink chamber 22 increases, and thus a viscosity of the ink decreases, thereby degrading ink ejecting characteristics of the printhead, such as an ink ejection frequency and an ink ejection rate.
Recently, line printing type inkjet printers have been developed to satisfy demands of high integration and high speed. Since an array printhead used in a line printing type inkjet printer includes many heaters, a large amount of heat is generated from the heaters and remains inside the array inkjet printhead. Accordingly, if a conventional thermal inkjet printhead is employed in the array printhead, ink ejection characteristics thereof may deteriorate. To solve the above problems, the remaining heat generated from the heater (i.e., the heat other than the heat used for ink ejection) should be dissipated inside the printhead or through a heat sink.